This invention relates to a process unit adapted to be removably mounted in a main assembly of a reproducing machine, the process unit comprising at least an imaging member and a charging device. The invention also relates to a reproducing machine, particularly a xerographic copying machine, including such a process unit.
Xerographic copying machines generally comprise two charging devices namely a charge corotron for initially charging the photoreceptor imaging member and a transfer corotron for attracting a toner image from the photoreceptor to a copy sheet. It is an important requirement that both corotrons are accurately and uniformly spaced from the photoreceptor in order to ensure a uniform charge distribution.
In Japanese Patent No. 0 109 371 to Kasama precise spacing between the corotron or a plurality of corotrons and the photoreceptor is achieved by having the corotron(s) pivotally mounted to the main assembly of the machine and the pivotable assembly is spring-biased towards the photoreceptor. With this arrangement the corotron(s) may be pivoted away from the photorecptor into a held-open position.
There is a trend now, however, to incorporate the photoreceptor together with other process means such as a charge corotron, a development device, and a cleaning device in a removable process unit or cassette as described, for example, in U.S. Pat. No. 3,985,436 to Tanaka et al. The use of such a cassette enables the easy replacement of those parts of the xerographic machine which are most likely to deteriorate with use, especially the photoreceptor, but also the development and cleaning systems as well as the charge corotron wire. A further advantage of containing the major xerographic process elements within a cassette is that interchangeable cassettes may be used in a given copying machine to provide different development characteristics or different coloured development.
Generally it is the case that the photoreceptor is located automatically in an operative position when the process unit is inserted into the main assembly of the copier, but there is still of course the requirement for the charging devices to be uniformly spaced from the photoreceptor.
Copending U.S. patent application Ser. No. 038,093 filed Apr. 14, 1987 entitled Process Unit For An Imaging Apparatus, in the name of Robert A. Carter, commonly assigned to the assignee of the present invention (our reference R/86003) concerns a process unit comprising a xerographic process cassette in which the imaging member, preferably in the form of a flexible belt photoreceptor, is only loosely retained in the process unit when the process unit is removed from the main assembly of the xerographic machine, and is adapted to be supported in an operative position by support means forming part of the main assembly when the process unit is inserted into the main assembly. This arrangement has the advantage of avoiding the need for any driving mechanisms within the cassette and also of making the insertion and withdrawal operations simple and reliable while ensuring that the photoreceptor is automatically positioned accurately relative to the optical system of the xerographic machine, but it does give rise to the problem of accurately locating the charging devices, i.e. the charge corotron and the transfer corotron, relative to the photoreceptor, because in the operative position the photoreceptor adopts a different position relative to the cassette as compared with its position when the cassette is removed from the main assembly of the copier.